Project Summary/Abstract Fine particulate matter <2.5 m (PM2.5) air pollution is the fifth leading risk factor for mortality worldwide. Over 88 thousand deaths per year are attributable to PM2.5 in the US alone, with the largest portion from cardiovascular (CV) causes (myocardial infarctions, strokes, heart failure). Despite improvements across the US, PM2.5 remains above World Health Organization Air Quality Guidelines (<10 g/m3) in numerous hot-spots (e.g., near roadways). Therefore, it is critical to develop feasible and effective personal strategies to protect ?vulnerable? (urban/near-roadway) and ?susceptible? (elderly) populations at risk from the harmful effects of PM2.5. Emerging trials have shown that portable indoor air filtration units (AFUs) with high-efficiency particulate arrestance filters can reduce PM2.5 exposures by 30-50% and improve CV health endpoints (e.g., BP, vascular function). Our recent clinical trial results confirm that even low PM2.5 levels pose significant risks to CV health and that portable indoor air filtration units (AFUs) represent a promising preventative strategy. However, no study has addressed whether exposure reductions and health improvements can be sustained over more clinically relevant periods of intervention (i.e., several weeks) which are required to plausibly yield decreases in actual CV events. In addition, the efficacy of the novel practical (i.e., less expensive and more feasible in real- world settings) approach of using a single AFU only in the bedroom to focus on reducing nocturnal PM2.5 exposure is currently unknown. This proposal seeks to conduct a randomized double-blind 3-way crossover intervention study (AFUs in 2 rooms vs. bedroom AFU use alone vs. sham filtration) in 50 adults living in a low-income senior residence impacted by roadway pollutants. Specific Aims are: (1) determine if long-term, 2-room AFU usage provides sustained reductions in PM2.5 exposure and persistent improvements in cardiometabolic outcomes; (2) determine if nocturnal PM2.5 exposure reduction alone improves cardiometabolic outcomes; and (3) demonstrate the key role of adrenal activation as a novel mechanism explaining PM2.5-induced cardiometabolic changes. Our proposal will help validate the benefits of novel strategies to employ AFUs in an elderly vulnerable population. Positive results would represent a key step in forming the evidence base required to promote more wide-scale AFU use; in the long term, given their low cost and burden, AFU use could be up- scaled to help protect diverse populations.